The present invention relates generally to pulse wave detecting devices and, more particularly, to a pulse wave detecting device for detecting a pulse wave by transmitting and receiving an ultrasonic wave to and from an artery.
It is common practice to detect a pulse wave from blood flow through an artery, at medical sites or in health care. Pulse wave detection is broadly conducted by electronically, automatically detecting a pulse frequency by using a pulse wave detecting device, besides detecting of a pulse frequency per a given time through palpation.
The devices which electronically detect a pulse wave and acquire a pulse frequency include those having a piezo-type piezoelectric element that is to be positioned as a sensor over an artery in order to detect a pulse frequency from a pressure change of a surface skin caused due to a an artery pressure change (surface skin displacement by pressure). There also exist those which detect a pulse frequency through use of an ultrasonic wave.
The pulse wave detecting devices using an ultrasonic wave includes those utilizing the Doppler effect due to blood flow, as proposed, e.g. in Japanese Patent Laid-open No. 214335/1989 and U.S. Pat. No. 4,086,916. That is, a change of frequency or phase in reflection wave can be detected by transmitting an ultrasonic wave toward an artery and receiving a reflection wave thereof by a receiving element. That is, while the artery is being expanded by a blood flow, a surface of the artery approaches the transmission source and receiving element, resulting in frequency increase due to the Doppler effect. Conversely, while the artery is contracting the frequency decreases. By detecting such a frequency or phase change, it is possible to detect a pulse wave and further a pulse frequency and blood flow velocity.
FIG. 2 shows a conventional pulse wave detecting device 5xe2x80x2. This structure has piezoelectric materials 2 forming an oscillation element to transmit an ultrasonic wave toward an artery and a receiving element to receive a reflection wave thereof. The piezoelectric materials 2 are covered with a resin 6.
In the conventional pulse wave detecting device, the ultrasonic wave transmitter and receiver are encapsulated by resin. When the pulse wave detecting device is put on a skin surface to detect pulsation, a gap delicately occurs between the surface skin and the pulse wave and air intrudes therein resulting in attenuation in an ultrasonic wave. It has been a conventional practice to apply gel between the surface skin and the pulse wave detecting device in order to prevent ultrasonic wave attenuation. However, such a method of applying gel between the surface skin and the pulse wave detecting device requires labor and time, including gel re-application when the ultrasonic wave again attenuates.
Meanwhile, in the conventional pulse wave detecting device, the resin-encapsulated transmitter and receiver are each formed by one planar PZT piezoelectric plate. Due to this, there is an adverse effect due to an angle given by the transmitter and receiver thus causing reduction of receiving sensitivity.
It is therefore an object of the present invention to provide a pulse wave detecting device which reduces noise to be caused due to attenuation of an ultrasonic wave.
Another object is to provide a structure to improve the receiving sensitivity in a pulse wave detecting device.
In accordance with the present invention, a pulse wave detecting device is provided comprising transmitting means for transmitting an ultrasonic wave toward an artery; receiving means for receiving the ultrasonic wave transmitted from the transmitting means; and wherein the transmitting means and the receiving means are provided protruding from a substrate.
That is, the transmitting means and the receiving means structurally protrude from the support substrate supporting the transmitting and receiving means. This allows the transmitting means and receiving means to be closely contacted with a surface skin of a wrist or the like without causing a slight gap. Thus, a pulse wave detecting device is realized that is less affected by noise. Accordingly, it is possible for the device to routinely detect a pulse wave while wearing it at any time in daily life.
Furthermore, at least one of the transmitting means and the receiving means is structurally covered with a matching layer formed of a resin or the like. This realizes a pulse wave detecting device which is highly matched in acoustic impedance and hence reduced in ultrasonic wave attenuation.
Also, a flexible board formed with a conductor pattern on a resin substrate may be used in place of the matching layer. That is, the flexible board realizes at the same time the matching of acoustic impedance by the resin substrate and the applying of an electric field to the transmitting means or receiving means by electrically connecting the conductor pattern to the transmitting or receiving means.
Also, isolation is structurally provided in the substrate mounting the receiving means and transmitting means. This provides a structure which prevents transmission of an ultrasonic wave generated by the transmitting means to the receiving means.
Also, the substrate uses a material designed to readily attenuate a ultrasonic wave. This enables efficient propagation of an ultrasonic wave toward an artery.
Furthermore, the transmitting means or the receiving means is made in an arcuate form. This eliminates the necessity to exactly adjust a parallelism between the transmitting means and the receiving means, facilitating ease of manufacture.
As described above, because the pulse wave detecting device is simple in structure, it can be routinely used by incorporating the pulse wave detecting device, for example, in a timepiece. In such a case, the transmitting means used for the timepiece can be partly utilized also as transmitting means for the pulse wave detecting device, further simplifying the structure.
Also, in the invention the transmitting means and the receiving means form one pair to provide a plurality of pairs on the support substrate. That is, although pulse wave detection is possible with one transmitter/receiver pair, a structure having a plurality of such pairs of detecting means enhances detectability of pulsation.
Also, an output means is structurally provided which acquires a pulse frequency as information about a pulse wave and outputs a pulse frequency. That is, pulsation is to be routinely checked.
Furthermore, a method for manufacturing a pulse wave detecting device is provided comprising a step of forming an electrode on a substrate and a process of selectively blowing ultrafine particles of a piezoelectric material onto the electrode to form a transmitter or a receiver.